Rocket hydrofuel container with chemical heating device



ROCKET HYDROFUEL CONTAINER WITH CHEMICAE HEATING DEVICE Filed 1m. 14,1954 INVENTOR. ROBERT E. COX

wan/M ATTOR Y United States Patent Ohio Filed Dec. '14, 1954, Ser. No.475,053 2 Claims. (Cl. 44-2) This invention relates to rocket motors andmore particularly to such motors utilizing molten metallic fuels. Anobject of this invention is to provide a means of readying jet motorsutilizing solid metallic fuels for operation in a relatively short time.

It has been proposed to employ metallic hydrofuels such as lithium,potassium, calcium, etc. and alloys of such metals as propellants forsuch rocket motors. These substances are referred to as hydrofuelsbecause of their spontaneous reaction with Water to produce gases usefulfor propulsion. Such metallic hydrofuels are solids at oldinarytemperatures; hence in order to render them useful as rocket hydrofuelsthey must be heated to the liquid state prior to operation. Thus, thefuel chambers of such rocket engines, as they have been used or proposedup to the present time, have required elaborate arrangements ofelectrical heating coils or other similar devices which require longperiods of time to complete the melting. For example, the melting of thehydrofuel in a typical tank of about 80 lbs. capacity has hithertorequired about two hours. i

The invention is carried out by positioning a heating tube in thehydrofuel tank in such a manner as to melt the hydrofuel when theheating tube is operated.

A feature is the provision of a non-gaseous heating composition whichupon combustion emits a relatively large quantity of heat to effectrapid melting of the hydrofuel.

The foregoing and other features of the invention will be betterunderstood from the following detailed description and the accompanyingdrawing of which:

FIG. 1 is a cross-section view taken at line 11 of FIG. 2 of a hydrofuelstorage tank containing a heating tube in accordance with thisinvention; and

FIG. 2 shows a cross-section view taken at line 22 of FIG. 1.

Referring to the drawing, there is shown a storage tank 16 of agenerally cylindrical shape containing a centrally located cylindricalheating tube 12. Although the cylindrical shape for tanks willordinarily be preferred, it should be understood that some other shapesuch as a square cross-section could be used. The heating tube 12contains a charge 13 of a substance which can be burned or reacted toproduce heat and the tank 16 can be filled almost to the top with asolid hydrofuel 17 such as lithium or any of the other hydrofuelsmentioned above, cast in the annular space around the heating tube 12.

The tank 16 is closed by top 22 and bottom 23 so that when the hydrofuelis in liquid condition, gas pressure can be applied at the inlet 18 toforce the liquid out the outlet 19.

Alternatively, propellant outlet 19 may be positioned at or near the topof the tank to permit the pumping of propellant as soon as meltingbegins.

A small amount of space is left empty inside fuel tank 16 to providespace for thermal expansion of the hydrofuel.

The heating tube 12 is closed at the bottom and the top opening isclosed by a cap 21 through which there is passed a cable 20 leading toan igniting squib 24 related to the heating composition 13.

The heating composition used in the heating tube should be one whichdoes not produce gas during its reaction; otherwise some provision wouldhave to be made for releasing the gas which may not always be convenientor desirable when the tank is used in a device under Water.

Because of weight and volume limitations in torpedoes, rockets, andother guided missiles it is necessary that the heating unit of thisinvention occupy only a minimum amount of space and be capable ofreleasing large quantities of heat per unit volume. These requirementspreclude the use of common commercially available heating compositionssuch as thermite and others used for such purposes as soldering, etc.because of their relatively low heat release per unit weight. At thesame time, it is essential that the amount of heat liberated is not sohigh as to result in damage to the heating tube itself.

I have found that an excellent composition for use as the heatgenerating element is provided by a mixture of finely divided aluminumand copper oxide. These substances react according to the followingequation:

2Al+ 3CuO- 3Cu+Al O +294 kilocalories This is equivalent to 1.0kilocalorie per gram or 5.1 kilocalories per cubic centimeter.

Other mixtures such as aluminum and lithium or potassium perchlorate,for example, will yield more energy, but unfortunately, it has beenfound impossible to contain this reaction in a sealed metal tube withoutthe use of special materials in the tube construction. The reaction of astoichiometric mixture of aluminum and copper oxide is also diflicult tocontain without the use of costly high melting metal containers,however, I have found that the reaction rate of aluminum and copperoxide can be slowed sufficiently by the incorporation of inert materialssuch as clay to permit its use in a tube composed of ordinary steel.

The admixture of such materials, however, may in some cases producedifiiculties in the burning rate characteristics of the grain, in thatburning may be irregular or incomplete due to the presence of such inertmaterials. I have found that the inclusion of small amounts of otheroxidizing materials such as thermite and potassium perchlorate as wellas oxidizing agents of comparable strength will correct this defect toprovide a grain which will burn in a uniform fashion and emit heatwithin usable limits.

I have found that a uniform mixture of from 65 to 36% by weight ofaluminum and copper oxide in stoichiometric proportions, from 25 to 60%by weight of thermite, and from 4 to 10% by weight of clay, provides aheating com position having the thermal and uniform burningcharacteristics required for use as the heating composition of thisinvention. In addition, I have found a second formulation also useful asthe heating composition of this invention which comprises from to 92% byweight of aluminum and copper oxide in stoichiometric proportions, from3 to 15% by weight of aluminum and potassium perchlorate instoichiometric proportions, and from 5 to 15 by weight of clay.

The following examples are provided to more clearly illustrate theheating compositions useful in the practice of this invention.

3 Example I Ingredients: Percent by wt. Al-Cu (stoichiometric) 56.1Thermite 37.4 Clay 6.5

Example ll Ingredients:

Al-CuO (stoichiometric) 83.3 AlKClO (stoichiometric) 4.4 Clay 12.3

For use in the heating tube, the foregoing heating substances arepowdered, dried, and mixed thoroughly, after which they can be pressedin sections in a suitable tube, such as a steel tube, at pressures inthe range of about 40,000 to 80,000 pounds per square inch until a solidgrain is obtained. A preferred compacting pressure is about 67,000pounds per square inch. The high degree of compression not onlyincreases the density of the grain, but also tends to reduce the burningrate which is highly advantageous in the case of a high energy burningmixture which has the tendency to melt the heating tube.

Since great heat is developed at the heating tube 12, this tube itselfshould be composed of a heat-resistant metal, such as steel. The tubematerial should have high thermal conductivity and ability to Withstandthe extremely high temperature developed by the combustion of thehigh-energy heating grains 13.

In operation the reaction or burning of the heating composition will beinitiated by electrical ignition of the squib 24. The heatingcomposition 13 will then commence burning at the end adjacent to thesquib, and the entire exposed surface area will react. This reactionwill progress down the length of the cylindrical grain of the heatingcomposition. Immediately upon ignition, the hydrofuel 17 in tank 16 willcommence to melt in the region adjacent the burning heating composition,this being the region immediately surrounding the cylinder 12. Thus,even though all of the hydrofuel in the tank 16 has not yet melted,there will nevertheless be enough of it in molten condition between theinlet and outlet conduits 18 and 19 so that the liquid hydrofuelpropellant is immediately available for use. This will permitsubstantially instantaneous use of the rocket engine with which it isassociated. The flow of the propellant will, of course, be initiated byapplying pressure at conduit 18 to force the liquid out the outlet 19into the rocket motor for use in a Well known manner.

The heating compositions of this invention burn at a rate ofapproximately 0.12 in./sec., hence an entire 80- 4- pound tank ofhydrofuel, such as lithium, can be melted in as little as three minutes.

In order to eliminate the possibility of contamination of the fuel bysmall particles of the heating composition such as those which mightresult from failure of the Wall of the heating tube, a small wire meshscreen may be interposed at propellant outlet 19 to separate suchparticles from the fuel.

To facilitate the flow of the molten hydrofuel even before it iscompletely molten, the outlet 18 can conveniently be carried into theinterior of the tank 16 into proximity with tube 12.

The heating tubes of this invention may be used either individually orin groups of two or more when it is desired to melt larger volumes orhigher melting metals.

I have found that each heating tube will melt approximately 15 times itsown volume of hydrofuels such as lithium and lithium alloys.

I claim:

1. A fuel unit for rockets which comprises a container substantiallyfilled with normally solid metal rocket hydrofuel, an inlet and anoutlet in said container, a heating tube within said container, a solidself-sustaining heating composition within said container, means forigniting said heating composition and pressurization means communicablewith said inlet for pumping said hydrofuel out of said container afterit has been converted to molten state by combustion of saidself-sustaining heating composition.

2. A fuel unit for a normally solid metallic rocket propellant fuelwhich comprises a container for said fuel, an inlet and an outlet insaid container, a heating tube within the said container, said heatingtube containing a solid self-sustaining heating composition and meansfor igniting said heating composition, said composition comprising auniform mixture and stoichiometric proportions of clay, copper oxide,aluminum, and an oxidizer selected from the group consisting ofpotassium perchlorate and ferric oxide.

References Cited by the Examiner UNITED STATES PATENTS 1,167,944 1/ 16Shurnan.

1,838,357 12/31 Bottrill.

2,016,407 10/35 WentZel.

2,020,101 11/35 Brown 266-39 2,040,407 5/3 6 Reed 44-3 2,152,446 3/39Temple 26639 2,352,951 7/44 Geria 443 X 2,680,063 6/54 Shapiro 44-3 CARLD. QUARFORTH, Primary Examiner.

ROGER L. CAMPBELL, WILLIAM G. WILES, REU- BEN EPSTEIN, Examiners.

1. A FUEL UNIT FOR ROCKETS WHICH COMPRISES A CONTAINER SUBSTANTIALLYFILLED WITH NORMALLY SOLID METAL ROCKET HYDROFUEL, AN INLET AND ANOUTLET IN SAID CONTAINER, A HEATING TUBE WITHIN SAID CONTAINER, A SOLIDSELF-SUSTAINING HEATING COMPOSITION WITHIN SAID CONTAINER, MEANS FORIGNITING SAID HEATING COMPOSITION AND PRESSURIZATION MEANS COMMUNICABLEWITH SAID INLET FOR PUMPING SAID HYDROFUEL OUT OF SAID CONTAINER AFTERIT HAS BEEN CONVERTED TO MOLTEN STATE BY COMBUSTION OF SAIDSELF-SUSTAINING HEATING COMPOSITION.
 2. A FUEL UNIT FOR A NORMALLY SOLIDMETALLIC ROCKET PROPELLANT FUEL WHICH COMPRISES A CONTAINER FOR SAIDFUEL, AN INLET AND AN OUTLET IN SAID CONTAINER, A HEATING TUBE WITHINTHE SAID CONTAINER, SAID HEATING TUBE CONTAINING A SOLID SELF-SUSTAININGHEATING COMPOSITION AND MEANS FOR IGNITING SAID HEATING COMPOSITION,SAID COMPOSITION COMPRISING A UNIFORM MIXTURE AND STOICHIOMETRICPROPORTIONS OF CLAY, COPPER OXIDE, ALUMINUM, AND AN XOIDIZER SELECTEDFROM THE GROUP CONSISTING OF POTASSIUM PERCHLORATE AND FERRIC OXIDE.